Consecutive atom reactions with molecules

Such behaviour clearly contrasts with the case of 4-iodoaniIine, where protonation in a chemical ionization source occurred not only on the ring but also on the nitrogen atom . Nitrogen protonation was indicated by ion-molecule reactions with dimethyl disulphide consecutive to collisional dehalogenation (FT-ICR experiments) or by an increase in the intensity of the peak at mjz 76 following high-energy collisional activation . 

The 62 c.v.e. /i/< -[Ru4(yU3-PPh)(CO)i3] cluster B has previously been shown to exhibit a rich and diverse chemistry in its reactions with alkynes and diynes (COMC (1995)). Reaction of the phospha-alkyne PCBu with B at room temperature gives [Ru4( 3-PPh) 3-PC(CO)Bu (CO)i3] 23 (Equation (18)). The PC(CO)Bu ligand contains a ketene unit resulting from attaek by a CO molecule on the coordinatively unsaturated C atom of the methylidyne unit. The Ru4 skeleton in 23 has a distorted Z chain that is consistent with its 66 c.v.e. count. The PC(CO)Bu ligand bridges three consecutive metal atoms the PPh unit bridges the two internal Ru atoms and the other terminal metal atom. ... 

Table I gives the compositions of alkylates produced with various acidic catalysts. The product distribution is similar for a variety of acidic catalysts, both solid and liquid, and over a wide range of process conditions. Typically, alkylate is a mixture of methyl-branched alkanes with a high content of isooctanes. Almost all the compounds have tertiary carbon atoms only very few have quaternary carbon atoms or are non-branched. Alkylate contains not only the primary products, trimethylpentanes, but also dimethylhexanes, sometimes methylheptanes, and a considerable amount of isopentane, isohexanes, isoheptanes and hydrocarbons with nine or more carbon atoms. The complexity of the product illustrates that no simple and straightforward single-step mechanism is operative rather, the reaction involves a set of parallel and consecutive reaction steps, with the importance of the individual steps differing markedly from one catalyst to another. To arrive at this complex product distribution from two simple molecules such as isobutane and butene, reaction steps such as isomerization, oligomerization, (3-scission, and hydride transfer have to be involved.

The idea of the evidence is rather simple and can be elucidated by means of the following experiment. Let us consider, for example, a molecule of 2-methylpentane labeled in a branched position by 13C 2-methyl- 13C(2)-pentane. If the consecutive reactions in the adsorbed state are with a given metal of low extent, and this is certainly true for Pt or Pd, then the appearance, among the product, of 3-methyl-l3C(3)-pentane is very strong evidence of the operation of the 5C (cyclic) intermediates. Only via a ring closure at one place and an opening at another place of the molecule can a label move simultaneously with the branch. On the other hand, when the branch and labeled atom become separated by isomerization, this is evidence of the operation of the 3Cay complexes (see Fig. 5). 

They proposed a polymerization scheme closely related to other well-known chemical reactions of metal alkoxide with carbonyl compounds (20). In Scheme 2, complex [A] is converted to [B] by hydride ion transfer from the alkoxyl group to the carbon atom of aldehyde (Meerwein-Ponndorf reduction). Addition of one molecule of monomer to the growing chain requires transfer of the alkoxide anion to the carbonyl group to form a new alkoxide [C]. Repetition of these two consecutive processes, i.e., coordination of aldehyde and transfer of the alkoxide anion, constitutes the chain propagation step. 

Manifestations of nuclei tunneling in chemical reactions in gaseous, liquid, and solid phases are consecutively considered in Sects. 4.2-4.5. Also discussed in this chapter are (1) manifestations of nuclear tunneling in the vibrational spectra of ammonia-type molecules (Sect. 4.6), (2) electron tunneling in gas-phase chemical reactions of atom transfer (the so-called "harpoon reactions, Sect. 4.2), and (3) tunneling of hydrated electrons in the reactions of their recombination with some inorganic anions in aqueous solutions (Sect. 4.4). 

The observations described prompted a study of the reaction between the 2-cyanoallyl anion and tetrafluoroethylene, since this system has the merit that the charge may be accommodated in the nitrile group of the reaction intermediate in the [2 + 3] atom cycloaddition (54). Elimination of two HF molecules indeed occurs, presumably in a consecutive way, although the product ions resulting from loss of one molecule of HF from the collision complex have not been observed (Dawson and Nibbering, 1980). However, reaction (54) has not yet been studied with specifically deuterated 2-cyanoallyl anions, so that at present an end-on addition process (55) cannot be excluded. 

Selective oxidation of hydrocarbons is of key importance in functionalization of hydrocarbon molecules. It is always a multi-step process with consecutive abstraction of hydrogen and addition of oxygen atoms. The difficulty of this reaction is, undoubtedly, that the process should go through these many steps, but also should stop at the desired product. Such requirements can be met by complex mixed-metal oxides, and the XPS characterization of two selected examples is briefly reviewed here. 

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